The present invention concerns novel succinimide derivatives of 2,5-dimercapto-1,3,4-thiadiazoles and their use as multifunctional additives for lubricating compositions.
Lubricating compositions ordinarily are formulated with various additives to enhance their performance. A problem sometimes encountered is that a particular additive has low solubility in oil or a combination of additives decreases the solubility of other additives in the lubricating composition resulting in undesirable haze or sediment formation. Therefore, it is desirable to use lubricating additives that can perform different functions.
The use of multifunctional lubricating additives containing the 2,5-dimercapto-1,3,4-thiadiazole group is known. 2,5-Dimercapto-1,3,4-thiadiazole is commonly called DMTD. Many DMTD derivatives have poor oil solubility and are incorporated into lubricating compositions with the aid of dispersants. However, dispersants employed in crankcase lubricating oils can degrade the elastomeric seals used in internal combustion engines. The dispersants can decrease the flexibility of the seals and increase their hardness causing crack formation.
Prior art dispersants include various nitrogen-bridged dispersants, including alkenylsuccinimide type. British Pat. No. 1,462,287 describes, among others, various succinimide dispersants which may be used to disperse dimercaptothiadiazoles having copper inhibiting activity. Specifically, a dispersant and 2,5-dimercapto-1,3,4-thiadiazole is interacted in amounts substantially greater than the stoichiometric amount necessary for salt formation. The precise chemical nature of the obtained homogeneous blends is not given. This intermediate blend can be reacted with a carboxylic acid to form a product of uncertain structure as described in U.S. Pat. No. 4,140,643.
Surprisingly, it has been discovered that certain amine dispersant derivatives of 2-(2-mercapto-1,3,4-thiadiazole-5-thio) succinic anhydride retain dispersant properties as well as display antiwear and antioxidant properties. The novel additives are compatible with elastomeric seals used in engines.